For updating the micom(3.08), you have to update the CPU(4.15.31) at first and then turn off/on the TV then update the micom.
If you don't to update the CPU at first, your TV might happen that TV doesn't turn on.
So. you must update the CPU and then update micom.
This is also same by using the IP SERVER with LGService.xml.
You must to update the CPU with LGService.xml as <type>IPK_FIRMWARE</type> at first. and then turn on the TV then update the Micom with LGService.xml as <type>PTC_FIRMWARE</type> then turn off/on.
You have to update the CPU and the MICOM separately with LGService.xml
You can downgrade in any order. But, We don't recommand to downgrade the firmware. If at all possible, update the latest firmware.